No abstract

Courtship songs in mice have been investigated to understand the mechanisms and ecological relevance of vocal communication. There is evidence that courtship song characteristics vary between different genotypes, but little is known on whether individuals, even within the same genotype, differ from each other in the composition, complexity, and temporal consistency of their songs. In a first study, we aimed to systematically identify song features typical of different genotypes, by assessing the composition and complexity (i.e., entropy) of the syllabic sequences of male laboratory mice from four different strains (Mus musculus f. domestica: C57BL/6J, BALB/c, DBA/2 and B6D2F1). Mice were individually presented with a swab containing fresh female urine for 5 minutes to elicit courtship songs. The four strains differed not only in the composition but also in the complexity of their syllabic sequences. In a second study, we investigated within-strain individual differences in temporal consistency and recurring motifs (i.e., identical sets of syllables that are repeated within a song), using BALB/c and DBA/2 mice. The same procedure as in the first study was followed, but in addition testing was repeated weekly over three weeks. Both strains showed some level of individual temporal consistency; BALB/c in the overall amount of emitted vocalisations and DBA/2 in the expression of specific syllable types. However, hierarchical cluster analysis revealed remarkable individual variability in how consistent song characteristics were over time. Furthermore, recurring motifs were expressed at varying levels depending on the individual. Taken together, not only genotype but also individuality can affect variability in courtship songs in mice, suggesting the existence of different courtship strategies (e.g., higher song consistency to facilitate individual identification) related to varying levels of behavioural plasticity.HIGHLIGHTSCourtship songs in mice can serve as a model to study vocal communicationWe explore how genotype and individuality affect courtship songs’ characteristicsGenotypes differ in composition and also in complexity of syllabic sequencesWe find remarkable individual variability in how consistent songs are over timeResults suggest the existence of variation in male courting behaviour

The neuregulin 1 (NRG1) ErbB4 module is at the core of an “at risk” signaling pathway in schizophrenia. Several human studies suggest hyperstimulation of NRG1-ErbB4 signaling as a plausible pathomechanism; however, little is known about the significance of stage-, brain area-, or neural cell type-specific NRG1-ErbB4 hyperactivity for disease-relevant brain endophenotypes. To address these spatiotemporal aspects, we generated transgenic mice for Cre recombinase-mediated overexpression of cystein-rich domain (CRD) NRG1, the most prominent NRG1 isoform in the brain. A comparison of “brain-wide” vs cell type-specific CRD-NRG1 overexpressing mice revealed that pathogenic CRD-NRG1 signals for ventricular enlargement and neuroinflammation originate outside glutamatergic neurons and suggests a subcortical function of CRD-NRG1 in the control of body weight. Embryonic onset of CRD-NRG1 in glutamatergic cortical networks resulted in reduced inhibitory neurotransmission and locomotor hyperactivity. Our findings identify ventricular enlargement and locomotor hyperactivity, 2 main endophenotypes of schizophrenia, as specific consequences of spatiotemporally distinct expression profiles of hyperactivated CRD-NRG1 signaling.

When confronted with ambiguous information, some individuals respond as expecting positive and others as expecting negative outcomes. Based on such decisions in ambiguous situations, a behavioural test was developed in animal welfare science that allows researchers to characterise animals as more “optimistic” or “pessimistic”. Recent studies using this judgement bias test detected consistent individual differences in “optimism levels”. However, the ecological and evolutionary relevance of these differences is not yet clear. In this proof-of-principle study with laboratory mice, we aimed to explore the potential ecological consequences of being more optimistic or pessimistic. Specifically, we investigated whether “optimists” make different foraging choices under predation risk than “pessimists”. To address this, we first characterised female mice (C57BL/6J) as more optimistic or pessimistic by using two established judgement bias tests. Then we assessed individual differences in the tendency to choose high-risk/high-reward or low-risk/low-reward conditions by using a newly developed test based on predator cues (rat odour). We show that this novel test is a suitable tool to investigate individual differences in ecologically relevant risk-taking: First, the test imposed a risk-foraging trade-off for mice because the risky condition clearly induced more avoidance and risk assessment. Second, individuals showed highly repeatable differences in their choice of the risky or safe option. Considering our main aim, we did not find evidence that optimistic and pessimistic mice make different foraging decisions under predation risk. A potential explanation is that optimists, although expecting positive outcomes, might not take more risks when it can jeopardise their survival.